Clerestory, in architecture, any fenestrated (windowed) wall of a room that is carried higher than the surrounding roofs to light the interior space. In a large building, where interior walls are far from the structure’s exterior walls, this method of lighting otherwise enclosed, windowless spaces became a necessity. One of the earliest uses of the clerestory was in the huge hypostyle hall of King Seti I and Ramses II at the Temple of Amon (1349–1197 bc, Karnak, Egypt), in which the central range of columns, higher than those on either side, permitted clerestories to be built of pierced stone slabs.

The clerestory of the Basilica of Constantine, Rome.

Alinari Archives/Corbis

In Roman architecture many great halls were lighted with clerestories. Usually, groined vaults over the central hall allowed large semicircular windows to be built above the side roofs, as in the tepidarium of the Baths of Diocletian (3rd century ad) and the Basilica of Constantine (ad 310–320), both in Rome. This device was used in Byzantine and Early Christian architecture, as exemplified by the clerestory walls under the side arches of Hagia Sophia in Constantinople (532–563).

The clerestory became most highly developed and widely used in the Romanesque and Gothic periods. The Chartres cathedral (1194), for example, has pairs of lancet clerestory windows that are almost as wide as the aisle windows.

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in Western architecture

...opened up as much of the wall surface as possible, producing areas of glazing that ran from the top of the main arcade to the apex of the vault. The combination of the triforium gallery and clerestory into one large glazed area had, of course, a unifying effect on the elevations. It produced an intricate play of tracery patterns and instantly unleashed an era of intense experiment into...

...elements are the arcade, the tribune (upper gallery set over the aisle and normally opening into the church) or triforium galleries (arcaded wall passages set above the main arcade) or both, and the clerestory. These may be given equivalent treatment, or one may be stressed at the expense of the others. Precedents for almost every conceivable combination existed in Romanesque architecture. In a...

...wall that supported the nave roof stood above the level of the side aisle roofs and could thus be pierced at the top with windows to light the centre of the church. This high nave wall is called the clerestory. The side aisles themselves were either single or double. The apse opened from the nave by a great arch known as the triumphal arch. In some cases, if there was a transept, another...